The present invention relates to the field of energy transfer measurement methods, apparatus, and systems. More specifically, the present invention relates to methods, apparatus and systems for measuring, and in some embodiments controlling, net energy transfer by radiation, convection and conduction through a fenestration, such as a window or translucent panel. The invention has applications in a variety of industrial and consumer fields, and it is emphasized that the background of the invention is discussed herein by way of comparison with merely one specific field of application, that of passive solar energy.
In the prior art, various systems have been proposed for operating solar heated buildings. For instance, it is known to use movable insulation to reduce heat loss through glazed openings such as windows, skylights, clerestories, and Trombe walls in a well-insulated building. Such movable insulation can be of hand operated variety, thermally sensitive type, or motor-driven type. Motor-driven applications are either manually activated or controlled by automatic timers, thermostats or light sensitive devices--examples are foam beads blown between double glazing, and motor-driven sliding insulation, blinds, or panels. Such systems feature relatively crude control of the insulation relative to the energy considerations which must be accounted for, thus wasting solar energy and consequently building heat.
In the passive solar heating of buildings, the solar energy should be turned on only when it is needed, so as to avoid overheating; and the solar energy should be turned off only when it is not needed, so as to avoid overcooling. Unfortunately, determining the threshold decision points is not a simple problem in the solar energy field. If the solar energy is to be controlled by movable insulation, it must be recognized that the highly time-variable solar radiation entering the building is accompanied by complex heat convection and conduction processes between building and environment, as well as reradiation. Unlike a furnace or electric heater which when energized always provides net heat energy flow from itself into the interior of the building, the control of the sun by means of movable insulation introduces variable radiation, convection, and conduction processes which often work at cross-purposes to each other. It is as if there is a "furnace" which can cool a building when it should be heating, and which can heat the building when it should be cooling, unless some means of accurate control can be found.
Accordingly, the accurate control of the timing of the use of solar energy in passively heated buildings is a significant problem, which a mere timer, wall thermostat, or light-sensitive cell is insufficient to solve. The reason is that accurate control depends on continuing knowledge of a quantity denominated herein as "net energy transfer (NET)". Net energy transfer is the actual solar energy available to pass into the building through a fenestration when the movable insulation is retracted or unblocked, net of losses by reradiation, convection, and conduction. Since an important advantage of passive solar energy is low cost, it is essential that the additional cost of such accurate measurement and control be kept small. Accordingly, the economical and convenient measurement of net energy transfer NET is an objective of the present invention.
Although it has just been stated that the ordinary wall thermostat is insufficient to provide the necessary accurate control of the solar energy, the consumer of energy usually finds it convenient and advantageously familiar to be able to control the building temperature by means of such a thermostat. Accordingly, it is a further objective of the present invention not only to accurately measure the net energy transfer NET through solar energy windows but also to control the solar energy with comparable convenience to the thermostatic manner in which natural gas, heating oil, and electric heating sources of energy in buildings are controlled in the prior art.
An additional problem in the solar energy field is accomplishing optimal control of more than one solar energy window in a passive solar building. In such a situation, it is not readily apparent whether all such windows should be blocked or unblocked at the same time, and if so when; or whether some windows should be blocked and others unblocked, and if so, which ones and when. Accordingly, it is a still further objective of the invention to provide accurate control for each additional solar energy window at relatively insignificant additional expense.
Other objectives and advantages of the present invention will be evident from the description of the invention hereinbelow.